Trends in Computed Tomography

This article appeared as an introduction to a Comparison Chart on Computed Tomography in the October 2013 issue.

With concerns about radiation dose and reducing unnecessary imaging scans, advances in computed tomography (CT) systems have brought about technologies such as iterative reconstruction software, intraoperative capabilities and dose-tracking software. In addition, recent studies on the use of CT on select patient populations and the modality’s benefits in detecting certain cancers are showing that the risks of CT imaging can go both ways. While CT exams can add to a patient’s lifetime exposure to ionizing radiation, they can also be more beneficial in cases where magnetic resonance imaging (MRI) or ultrasound might not be able to detect early-stage cancers. Some of these trends in utilization indicate that appropriate low-dose CT imaging will be key across patient populations.

Use in Pediatric Imaging

The Image Gently campaign, first established in 2007, has called attention to the growing use of CT scans on pediatric patients. A report published June 2013 online in JAMA Pediatrics found that reducing unnecessary CT scans of children and lowering doses for the highest-dose scans could lower the overall lifetime risk of future imaging-related cancers by 62 percent.[1] Researchers at the University of California (UC) Davis Health System, led by lead study author Diana Miglioretti, dean’s professor in biostatistics in the department of public health sciences at UC Davis Health System, studied CT utilization trends in both male and female children under age 15 in six healthcare systems in the United States between 1996 and 2010.

The retrospective study examined random scans of the head, abdomen/pelvis, chest and spine; all are regions of the body that account for more than 95 percent of all CT scans, according to the researchers. They found that use of CT in children increased between 1996 and 2005, and that radiation doses varied for exams of the same anatomy. “There are potential harms from CT, meaning that there is a cancer risk, albeit very small in individual children,” said Miglioretti in a press release.

Using that data, the researchers calculated the projected risk of future cancers using the Biological Effects of Ionizing Radiation (BEIR) VII report for common cancers such as brain, liver, lung and prostate. The risk for radiation-induced leukemia and brain cancers were highest for scans of the head, the most commonly performed CT scan in children, according to the report. Given the risks, it is also important to note the value of using low-dose CT to image children when necessary.

Lung Cancer Screenings

Low-dose CT is seeing increased possibilities for use as beneficial screening for those at risk of lung cancer. In July 2013 the U.S. Preventive Services Task Force (USPSTF) recommended a high “B” rating for annual CT scans of current and former smokers who meet certain criteria.[2]Those 55 to 80 years old, who have a 30 pack-year or greater history of smoking, and are either current smokers or have quit in the past 15 years, may soon be able to seek regular CT lung screening. The USPSTF rating can also add to the push for screening to be covered by insurance, including Medicare.

The draft recommendation came about after results from the National Lung Screening Trial (NLST) were published in the New England Journal of Medicine in May. The NLST is a large-scale clinical trial that randomized more than 53,400 participants at high risk for lung cancer into either a CT arm or standard chest X-ray arm. The report’s authors found there was a 20 percent reduction in lung cancer deaths among participants screened with CT versus those who had chest X-rays. These initial results from the trial reflected those of other trials that compare the effective use of CT with X-ray in detecting early-stage lung cancer, said the authors.

In addition, advances in chest CT are helping to make the case for screening. Alignment technology can enhance exams by offering more accurate and timesaving comparisons for radiologists who must assess lung nodules across exams for change, often complicated by variances in patient positioning and breath hold. In the Stony Brook study to be published later this year, researchers measured the time it took for radiologists to match each nodule in prior exams to the same location in current exams using both manual alignment and automatic alignment software.[3]

The study used Blackford Analysis’ automatic alignment software integrated with picture archiving and communications systems (PACS), and compared it to a manual method where radiologists scroll manually to match lung nodules. Preliminary data announced in August shows that automatic deformable alignment can reduce location match time by greater than 55 percent. These results may have an impact on the workloads of radiologists, who may face an increase in chest CT studies for lung cancer following the USPSTF’s announcement, said Ben Panter, CEO of Blackford Analysis.

New Systems

Some of the latest CT systems offered by vendors are equipped with technologies to lower dose and provide image quality comparable to that of high-dose scans. The NeuViz 64 from Neusoft Medical Systems Co. Ltd. delivers low-dose scanning, high patient throughput and ease of use, and is equipped with technologies to improve resolution, reduce artifact and noise, and deliver pediatric-specific protocols.

One of Siemens Healthcare’s latest offerings is the Somatom Perspective, a 128-slice CT scanner that received U.S. Food and Drug Administration (FDA) clearance in June 2012. It includes Siemens’ SAFIRE (sinogram affirmed iterative reconstruction) technology and an exclusive eMode feature that determines and automatically selects system scan parameters so the scanner operates with as low a load as possible.

Toshiba’s Aquilion Prime is designed to be a more scalable and adaptable CT system, with advanced dose reduction iterative construction technology and a high-capacity couch that can move laterally and is low to the ground. A new platform for the Aquilion One family of CT scanners is set to display at the annual meeting of the Radiological Society of North America (RSNA) in December.